The present invention relates to optical bus systems and, in particular, it concerns a fiber optic free-space optical link.
It is known to employ optical buses to facilitate the high rate of data transferal required by some of the newer processing components. The issue of optical buses is relevant to new system with back planes designed specifically for such buses, as well as retrofitting or upgrading existing hard wired back planes using electronic buses.
U.S. Pat. No. 5,204,866 discloses an electronic system consisting of a number of subsystems or electronic components, which are connected by an optical bus. The individual electronic components are arranged in a housing in such a manner that optical interface units disposed on each component form a monoaxial, bidirectional optical bus working in free-space which distributes electrical signals among the individual components. These signals are transmitted along a single linear axis as polarized light beams. Here each individual component has a bus interface unit for generating outgoing light beams and receiving incoming beams along both directions of the axis respectively. The interface units use laser generators, photodetectors and amplitude-beam-splitters.
In spite of an improvement in the technique, however, such systems are still cost-intensive and only allow for compact construction to a very limited extent, since each individual component requires optical interface units. Furthermore, systems of this type display lower reliability due to the large number of optical elements used. It should also be noted that this type of system is better suited for new systems, since it would be difficult to retrofit an existing system with appropriately aligned housings due to height and location problems created by the existing electronically licked boards.
U.S. Pat. No. 6,038,355 discloses an optical bus between circuit boards or other devices. The system features an electronic circuit assembly that includes electrical circuitry associated with two beam splitters having different optical axes, a detector responsive to one optical axis, and an optical output configured for optical input on the other optical axis.
U.S. patent application Ser. No. 2003/0081281 concerns a Wavelength Division Multiple Access (WDMA) free-space broadcast technique for optical backplanes and interplanar communications for providing free-space optical interconnects between multiple circuit cards in a computer system or networking device. It is intended to provide a stable, optimal alignment between a laser center wavelength and the center of a Gaussian bandpass filter in order to optimize power transmission through free-space and reduce optical crosstalk interference in optical networks.
Although the systems referred to above may function as intended when deployed as per design specifications, they do not address the issue of functionality when alternative deployment is required, such as during debugging of the system or an individual board. That is, the required optical alignment is attainable only when the board is in a “normal” deployment on the backplane.
U.S. Pat. No. 6,580,865 offers a system by which individual boards are placed in optical communication by stringing one or more optical fibers from one board to the next. Several boards along a backplane are thus interconnected in series. Although not specifically mentioned in the document, it will be obvious to one skilled in the art that an unintended side benefit of this system in the ability to debug components while they are out of their normal position on the backplane. Drawbacks to this system, however, include being deployable only in systems which have enough room for the user to physically maneuver so as to attached the optical fibers in their receptacles, and the time required to perform detachment and attachment of fibers when a component board is replaced.
In some applications, although the need to replace boards is infrequent, when it is required speed is of the essence. Such applications may include aviation on-board flight control system, ground based flight tracking systems, military applications such as high technology weaponry and detection systems, to specify a few.
There is therefore a need for a fiber optic free-space optical link in which data is transmitted through free-space between open ends of optical fibers.